Illumination systems configured to produce a train of light pulses that are repeated at high frequency may be used for various artistic, medical, technological, military, and scientific applications. Generally, the illumination systems comprise a semiconductor light source such as a light emitting diode (LED) or a laser diode (LD) encapsulated in a protective package having electrically conducting leads or pads for coupling the light source to a source of power. As semiconductor light sources convert only between about 10% to about 50% of energy they receive to useful optical output, a large balance of the energy they receive is converted to heat, which must be dissipated to prevent their damage and enable their efficient operation. Typically, the light sources are mounted to a thermally conducting submount for conducting heat that they generate during operation to a suitable heat sink.
By way of an illustrative example application, a gated time of flight (GT-TOF) range camera may use such an illumination system to illuminate a scene that it images with a train of light pulses to acquire a “range image” of a scene that provides distance measurements to features in the scene. Following transmission of each light pulse in the light pulse train, the GT-TOF camera gates ON for a short exposure period during which pixels in a photosensor of the camera are sensitive to, and register light incident on the pixels. During the short exposure period following a light pulse, a pixel imaging light from a given feature in the scene registers an amount of light that the given feature reflects from the light pulse back to the camera. The camera uses an amount of reflected light that the pixel registers for the given feature during the exposure periods from, typically, all the light pulses in the light pulse train to determine a round trip time for light to travel from the camera to the given feature and back to the camera. The round trip time for the feature and the speed of light are used to determine a distance to the feature.
Light pulses in a light pulse train that a light source in a GT-TOF camera transmits to illuminate a scene that the GT-TOF camera images and exposure periods of the camera may have pulse widths as short as a few nanoseconds and repetition frequencies greater than a megahertz (MHz). As it is generally advantageous to acquire a range image of a scene in as short a time as possible, it is advantageous that a number of light pulses in the light pulse train and associated exposure periods be as small as possible. However, as pulse widths get shorter and repetition rates faster, it can be technically challenging to generate the light pulses with sufficient intensity and pulse shape uniformity so that distance measurements provided by the GT-TOF camera have acceptable accuracy and signal to noise ratios (SNR). Cost considerations and heat dissipation requirements for maintaining the light source and the camera at acceptable operating temperatures usually limit intensity of illumination provided by the light source. The fast switching demands mandated by short pulse widths and high repetition rates of light pulses that the light source generates, and common constraints that electronic and optical components of systems have small footprints compound the challenges.